Oscillators are utilized in a large number of electronic equipment, including communications systems (e.g., wireless and wireline), entertainment electronics, aerospace systems, and timing systems. Oscillators can be utilized to provide a reference signal (e.g., a clock signal) for processing occurring in the electronic equipment. Due to the type of use of the oscillators, precision of the signal frequency associated with the oscillator can be a significant requirement.
Crystal oscillators having quartz crystals as the resonating element often are utilized in the electronic equipment because they are often capable of being manufactured to provide signal frequencies within ±1.5 parts-per-million (ppm) of a target frequency value, frequency stabilities of ±2.5 ppm over an operating temperature range from −40° C. to +85° C., aging of below ±1 ppm/year (at 25° C.), typical phase noise of −138 dBc/Hz at 1 kHz, and power consumption as low as 1.5 mA.
Various industries have developed standards and protocols that are based on use of particular or standard frequencies for reference signals and clock signals. For instance, frequency values can be as low as 32.768 kHz for watch crystals and real time clocks. Frequencies in the MHz range are commonly used in cell phones and GPS receivers, including 12.6 MHz, 13 MHz, 14.4 MHz, 16 MHz, 16.368 MHz, 16.9 MHz, 19.2 MHz, 19.8 MHz, 20 MHz, 23.104 MHz, 24.554 MHz, 26 MHz, 27.456 MHz, 32 MHz, 33.6 MHz, 38.4 MHz, and 52 MHz. Owing to the ability to manufacture quartz crystals to provide a desired target frequency, crystal oscillators are often manufactured to provide one of the several standard frequencies. Systems and circuits receiving signals from crystal oscillators are often designed to work with one of the standard frequencies corresponding to the particular crystal oscillator being utilized.
As an example, FIG. 1 illustrates a conventional apparatus 100 including an oscillator 102 coupled with a system 106. An input port 105 of the system 106 receives an oscillator signal 104 output from an output port 103 of the oscillator 102. In this example, the system 106 is designed to work with a signal of precisely 26 MHz. Therefore, a 26 MHz oscillator is selected for the oscillator 102. If the system 106 receives a different frequency, it may not operate properly.
Fractional-N phase lock loops are at times utilized in contemporary devices since they can at times compare at a high frequency, and can at times reduce phase noise due to the phase frequency detector operating at a higher frequency and the multiplication factor being lower. Due to the use of a sigma delta modulator to toggle divider settings both, phase noise and spurious emissions may also deteriorate significantly at narrower step sizes.
In the drawings, the same reference numbers identify identical and/or substantially similar elements or acts. The drawings illustrate particular embodiments for the purpose of describing the present disclosure, and are not intended to be exclusive or limiting in any way. The figures are schematic and are not intended to be drawn to scale. In the figures, each identical, or substantially similar component that is illustrated in various figures is represented by a single numeral or notation. For purposes of clarity, not every component is labeled in every figure. Nor is every component of each embodiment of the present disclosure shown where illustration is not necessary to allow those of ordinary skill in the art to understand the disclosure.
In the course of the detailed description to follow, reference will be made to the attached drawings. These drawings show different aspects of the present disclosure and, where appropriate, reference numerals illustrating like structures, components, materials and/or elements in different figures are labeled similarly. It should be understood that various combinations of the structures, components, materials and/or elements, other than those specifically shown, are contemplated and are within the scope of the present disclosure.